1. In the laboratory you dissolve 23.1 g of iron(II) nitrate in a volumetric flask and add water to a total volume of 500 mL.

What is the molarity of the solution?  M.

What is the concentration of the iron(II) cation?  M.

What is the concentration of the nitrate anion?  M.

2. In the laboratory you dissolve 13.6 g of iron(III) bromide in a volumetric flask and add water to a total volume of 125 mL.

What is the molarity of the solution?  M.

What is the concentration of the iron(III) cation?  M.

What is the concentration of the bromide anion?  M.

3.
You need to make an aqueous solution of 0.212 M zinc chloride for an experiment in lab, using a 500 mL volumetric flask. How much solid zinc chloride should you add?

4.

How many milliliters of an aqueous solution of 0.125 M ammonium nitrate is needed to obtain 4.33 grams of the salt?

mL

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ceruleandinosaur482

You weigh out a piece of copper wire (AW=63.546):
Weight of copper standard....................0.2437 g
Dissolve it in a slight excess of concentrated nitric acid. Add tothe solution the required amount of concentrated ammonia. Transferthis quantitatively to a 100 mL volumetric flask, dilute to volume,and mix thoroughly.
10.00 mL of this is pipetted into a 100 mL volumetric flask, therequired amount of concentrated ammonia is added and diluted tovolume. This is Standard 1.
Standard 2 is made by pipetting 20 mL of the original solution intoa 100 mL volumetric flask, adding the required amount of ammonia,NH3, and diluting to volume.
Using the same cuvet for all measurements, the following %T's wereobtained at 625 nm:
Blank 101.3 %
Standard 1 61.0 %
Standard 2 35.5 %

Next:
You pipetted 10 mL of UNKNOWN into a 100 mL volumetric flask. Therequired amount of ammonia was added and the mixture diluted tovolume. The %T of this solution was measured at 625 nm, using thesame spectrometer and cuvet as for the standards.
%T unknown.................... 21.4 %
CALCULATE
a) The absorbance of Standard 1 ______________
b) The absorbance of Standard 2 ______________
c) The molarity of Cu in Standard 1 ______________ M
d) The molarity of Cu in Standard 2 ______________ M
e) Ratio: absorbance/molarity Std 1 ______________
f) Ratio: absorbance/molarity Std 2 ______________
g) Average ratio of absorbance/molarity ______________
h) Absorbance of unknown solution ______________
Concentration of copper in unknown...
i) solution as measured in cuvet ______________ M
j) in original solution ______________ M
k) in original solution ______________ w/V%

Finally:
You are given a solid UNKNOWN, containing copper, weighing........0.7937 g.
You dissolve this in concentrated Nitric Acid, HNO3, transferquantitatively to a 100 mL volumetric flask, add the requiredamount of Ammonia, NH3, dilute to volume and mix thoroughly.
This resulting solution is too concentrated and the resulting %Tmeasured in the same cuvet and spectrometer as before gave littleor no transmission (<10%). br="">You are told topipet.................... 16.00 mL
into a 100 mL volumetric flask, add the required amount of ammonia,dilute to volume and mix.
Spectroscopic measurement of this solution gave %T... 35.6 %
CALCULATE:
l) Absorbance of the dilutedsolution....................._____________________
m) The copper concentration in the dilutedsolution...._____________________ M
n) The copper concentration in the originalsolution..._____________________ M
o) The Per Cent copper in the original solidUNKNOWN..._____________________ % Cu

azuresea-lion948

You weigh out a piece of copper wire (AW=63.546):
Weight of copper standard....................0.2437 g
Dissolve it in a slight excess of concentrated nitric acid. Add tothe solution the required amount of concentrated ammonia. Transferthis quantitatively to a 100 mL volumetric flask, dilute to volume,and mix thoroughly.
10.00 mL of this is pipetted into a 100 mL volumetric flask, therequired amount of concentrated ammonia is added and diluted tovolume. This is Standard 1.
Standard 2 is made by pipetting 20 mL of the original solution intoa 100 mL volumetric flask, adding the required amount of ammonia,NH3, and diluting to volume.
Using the same cuvet for all measurements, the following %T's wereobtained at 625 nm:
Blank 101.3 %
Standard 1 61.0 %
Standard 2 35.5 %

Next:
You pipetted 10 mL of UNKNOWN into a 100 mL volumetric flask. Therequired amount of ammonia was added and the mixture diluted tovolume. The %T of this solution was measured at 625 nm, using thesame spectrometer and cuvet as for the standards.
%T unknown.................... 21.4 %
CALCULATE
a) The absorbance of Standard 1 ______________
b) The absorbance of Standard 2 ______________
c) The molarity of Cu in Standard 1 ______________ M
d) The molarity of Cu in Standard 2 ______________ M
e) Ratio: absorbance/molarity Std 1 ______________
f) Ratio: absorbance/molarity Std 2 ______________
g) Average ratio of absorbance/molarity ______________
h) Absorbance of unknown solution ______________
Concentration of copper in unknown...
i) solution as measured in cuvet ______________ M
j) in original solution ______________ M
k) in original solution ______________ w/V%

Finally:
You are given a solid UNKNOWN, containing copper, weighing........0.7937 g.
You dissolve this in concentrated Nitric Acid, HNO3, transferquantitatively to a 100 mL volumetric flask, add the requiredamount of Ammonia, NH3, dilute to volume and mix thoroughly.
This resulting solution is too concentrated and the resulting %Tmeasured in the same cuvet and spectrometer as before gave littleor no transmission (<10%). br="">You are told topipet.................... 16.00 mL
into a 100 mL volumetric flask, add the required amount of ammonia,dilute to volume and mix.
Spectroscopic measurement of this solution gave %T... 35.6 %
CALCULATE:
l) Absorbance of the dilutedsolution....................._____________________
m) The copper concentration in the dilutedsolution...._____________________ M
n) The copper concentration in the originalsolution..._____________________ M
o) The Per Cent copper in the original solidUNKNOWN..._____________________ % Cu

CHEM 121 Midterm: CHEM 121 Midterm 1 2010

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